No sir, I do not consider that normal operation.
The weather is too warm outside at 40° to be freezing in this manner.
What you see here are four White stripes that indicate there are four circuits to the outdoor coil. Each of these circuits are fed by small distribution tube after it passes through some form of metering device.
This metering device can be a device such as the carburetor on your car that changes the amount of gas passing through it depending on the load requirements. A second type device is an “accurator” which is a small piston with a properly sized hole that controls the amount of refrigerant passing into the coil. This type is most commonly found as the heat pump load is relatively stable at low outdoor temperatures.
This Frost pattern is an indication of a “starved outdoor coil” which can be indicative of a low refrigerant charge and/or an improperly sized accurator, a restricted orifice in the accurator (or in the event that you have a thermal expansion valve (the carburetor type device) where there are several things that could go wrong here.
First of all we must determine that the refrigerant charge is adequate according to manufacturer specifications.
If there is a restriction in the accurator, adding more refrigerant will not change anything.
If you add refrigerant and the frosts goes away, that was the problem.
The problem with heat pumps in the winter time is it there is no accurate way to determine the refrigerant charge without actually weighing the charge. If testing the refrigeration pressures according to the manufacturers charts does not show proper pressures for existing conditions, the refrigerant should be removed and weighed.
A further explanation of what is going on here is that refrigerant is actually being sucked through the outdoor coil by the compressor. If there is a low refrigerant charge or a restriction in the metering device the refrigeration pressures of the outdoor coil will go extremely low. Low pressure results in low temperature (resulting in the frosted lines). Proper charging and metering of the refrigerant through this coil should saturate the coil and provide an even Frost pattern from top to bottom under normal operation.
In the area where the frost is, you are converting liquid refrigerant to a vapor, absorbing large quantities of heat in the process. Once you’ve run out of liquid refrigerant and the vapor becomes superheated, it can not collect any more heat so the coil doesn’t frost on the remainder of the circuit.
Another issue that you’re experiencing is improper defrost. The coil freezes up solid after it runs long enough and does not automatically defrost. This is due to improper temperatures where the sensors are and possibly insufficient refrigerant charge to generate enough heat to melt the ice from the coil in an expedited manner controlled by the defrost computer.
Any HVAC contractor that’s worth squat with heat pumps should be able to readily determine what’s going on.
Considering your previous question about bad soldering techniques diagnosed by your HVAC contractor, the only soldering that is done during installation is at the lower two areas in the picture below.
The quality of workmanship from these photographs appears normal.
The other two areas indicate one individual circuit which is operating under approximately 50% capacity.